This invention relates to power supplies employing D.C.-A.C.-D.C. conversion and more specifically to such power supplies capable of being connected in variable numbers to a power bus for meeting various output power requirements. The design of the basic power unit which is used in this modular system of load sharing power supplies is also described in U.S. Ser. No. 593,070, filed July 3, 1975 now U.S. Pat. No. 4,032,830 and entitled Modular Constant Current Power Supply.
Circuitry for accomplishing D.C.-A.C.-D.C. power conversion is well-known in the art. Such circuits generally employ switching means such as power transistors or SCR's set up to modulate an unregulated D.C. supply level. The modulation is accomplished by either clock-driving the power switching means or configuring the power switching means in self-oscillating circuits. It is also generally known to provide feedback of the output voltage of such circuits to control either the frequency or duration of the excitation of the converter switching elements. Such use of feedback is illustrated in the converter circuits of U.S. Pat. No. 3,824,441 issued to Heyman et al. on July 16, 1974 and U.S. Pat. No. 3,670,234 issued to Joyce on June 13, 1972.
However, none of these prior art circuits have exhibited sufficient responsiveness to changing output load conditions to enable them to be practically used in multiple configurations to provide varying amounts of power required by diverse loads. Particularly in the area of computer systems where diverse system size and power requirements exist, the flexibility attainable from a modular power supply has appeared to be of immeasurable value, especially in eliminating excessive costs required to adapt power supplies to various load requirements.